In certain types of memory, such as a read only memory (ROM), memory cells are arranged in an array of n rows by m columns. During the manufacturing process, transistors are selectively constructed in the memory cells, depending upon an intended pattern. During operation, all column lines are periodically precharged. When a particular row is selected, if a transistor has been constructed in column j of that row, then column j will be discharged, thus consuming power during the next precharge cycle. In general, the greater the number of transistors constructed in the memory array portion of the ROM, the greater the amount of power that will be consumed during the operation of the ROM. In addition to the increased actual electrical current requirements, the increased power consumption requires commensurately higher heat dissipation capabilities.
With more and more electrical and computational equipment using batteries as their primary source of power, it is becoming increasing important to reduce the power consumed. In particular, for microcontrollers using on-board ROM, it is important to reduce the energy utilized by the ROM as much as possible. The reduction in power is also useful for applications in which a standalone ROM integrated circuit is used.